1. Field of the Invention
This invention relates generally to interconnections and optical protection in optical communication networks.
2. Description of Related Art
Recently, optical communications have become established as a next generation communication technology. Advances in optical fibers that carry optical data signals, and in techniques (e.g., wavelength division multiplexing (WDM)) for efficiently using the available bandwidth of such fibers, have caused optical technologies to be utilized in state-of-the-art long haul communication systems. As used herein, “WDM” may include either or both of the functions of multiplexing (i.e., multiple signals into one signal) and demultiplexing (i.e., one signal into multiple signals).
Depending upon the relative locations of the data source and the intended recipient, optical data signals may traverse different optical communication systems between the two locations. One example of this occurs in trans-oceanic (e.g., trans-Atlantic) data connections. For example, optical signals may travel along both a terrestrial optical communication system and a submarine optical communication system.
FIG. 1 is a schematic diagram of an exemplary optical communication system 100 that includes an undersea, or submarine, portion. The optical communication system 100 may include two land-based, or terrestrial, WDM terminals 110 and 140 that are connected by a submarine optical fiber 120, perhaps in the form of an undersea cable. The submarine optical fiber 120 may connect to one or more line units 130 that are used to amplify the optical signal in the fiber 120. Line units 130 are also sometimes referred to as “repeaters.” Although communication may be shown in one direction in FIG. 1 and elsewhere herein, those skilled in the art will appreciate that communication may be bi-directional, for example by using a pair of optical fibers or other known methods of bi-directional optical communication.
For “long haul” (e.g., greater than or equal to several hundred kilometers) optical communications, the optical signal may be periodically amplified to compensate for attenuation in the fiber 120. As many line units 130 are used as necessary to amplify-the transmitted signal so that it arrives at WDM terminal 140 with sufficient signal strength (and quality) to be successfully detected and transformed back into a terrestrial optical signal. The terminals 110 and 140 may contain all of the components needed to process the terrestrial optical signals to and from submarine optical signals.
FIG. 2 is a block diagram of an exemplary terminal unit 110 of the optical communication system 100. The terminal unit 110 may include long reach transmitters/receivers (LRTRs) 210, WDM and optical conditioning equipment 220, link monitor equipment 230, line current equipment 240, a backplane 250, and a network management system 260. All of this equipment has typically been housed in one or more cabinets (not shown) disposed at a cable landing site (also referred to as a cable landing station, or merely “cable station”) near the point at which the undersea cable 120 exits the submarine optical communication system.
The LRTRs 210 may be configured to convert terrestrial optical signals into an optical format suitable for long haul transmission. The LRTRs 210 also may be configured to convert the undersea optical signal back into its original terrestrial format and provide forward error correction for the submarine line. The WDM and optical conditioning unit 220 may be configured to multiplex and amplify the optical signals in preparation for their transmission over cable 120 in a transmitting direction. In the opposite (i.e., receiving) direction, the WDM and optical conditioning unit 220 may demultiplex optical signals received from cable 120. The link monitor equipment 230 may be configured to monitor the undersea optical signals and undersea equipment for proper operation. The line current equipment 240, which may also be referred to as power feed equipment (PFE), provides power to, for example, the undersea line units 130 coupled to the undersea cable 120.
As these optical systems are upgraded and/or new submarine optical communication systems are deployed, the number of channels and number of optical fibers associated with each system may increase dramatically. Retrofitting existing cable landing stations to handle new equipment may not be commercially feasible. At the same time, acquiring new landing sites may be equally challenging. In the related application, techniques for modifying or adding system equipment, while minimizing cable landing station access and space usage are described.
In addition to minimizing cable landing station access and space usage, it would further be desirable to provide techniques and architectures which will permit two faults to be handled when submarine rings are connected to terrestrial backhauls.
For underwater optical networks, a additional problem exists in shallow waters due to dragging boat anchors and the like, which may make contact with fiber optic lines and thereby cause damage or cuts to those lines. This problem also may occur for land-laid optical networks, whereby certain portions of fiber optic cable laid below ground are more susceptible to damage than other portions of the fiber optic cable. For example, if a fiber optic cable is provided between Baltimore, Md. and New York, N.Y., then there is a higher probability of damage to the fiber optic cable located at the two cities, due to building and road construction and repair, than along locations between the cities in which the fiber optic cable is laid.
Presently, fiber optic systems use one of two schemes that incorporate path diversity in regions where there is a high probability of fiber cut. In one scheme, fiber bundle legs are split at branch units and half of the fibers are routed along two different paths. In the other scheme, each wavelength division multiplexed (WDM) fiber is split/combined at the branch units by wavelength using wavelength splitters and combiners. In either case, half of the bandwidth is routed over two separate diverse paths. If one of the two fiber bundles is cut in the region where there is a high probability of fiber cuts, half of the total bandwidth is lost in the region where there is a low probability of fiber cuts. Accordingly, there is a need for a fiber optic system using a branch unit to route entire fiber bundles diversely, to avoid losing half of the bandwidth when one or more of the fiber bundles is damaged in the region where there is a high probability of fiber cuts.
Typically, conventional optical communication systems comprise a receiving node and a transmitting node (Baltimore, Md. and New York, N.Y. in the aforementioned example) connected via optical fiber. Each node contains equipment for communication via optical fiber. Such equipment includes channel equipment and WDM equipment. A fiber-bay comprises channel equipment and WDM equipment. Channel equipment is equipment that transmits and receives via a specific channel. A line unit is a repeater that optically amplifies WDM signals on an optical fiber.
Also, for fiber optic networks, problems in transmitting and receiving signals may be due to equipment failure, such as switch failure, or it may be due to failure of the signal lines, such as the fiber optic lines which provide signals from a source to a destination.
Typically, conventional optical communication systems comprise a receiving node and a transmitting node connected via optical fiber. Each node contains equipment for communication via optical fiber. Such equipment may include channel equipment and Wavelength Division Multiplex (WDM) equipment. Channel equipment is equipment that transmits and receives via a specific wavelength (or channel). In a conventional system, if a fiber is cut resulting in a loss of signal, the system requires a network element (such as a SONET processor) to determine there is a failure in the digital domain and notify the switch to change state.
Further, switches are utilized to direct signals transmitted by the nodes to various fiber optical cables within a conventional optical communication system. When a switch fails in a conventional system, an operator manually reconfigures the switch to communicate via an alternate channel. The resulting down time from manually switching channels results in a high amount of data loss and an inefficient use of backup resources.